On the basis of complex studies, carried out over the period of 21 years, the epidemiological characterization of Yersinia infections in the Republic of Sakha (Yakutia) is presented. The average monthly morbidity rate (per 100,000 persons) was 5.8 +/- 0.002 for pseudotuberculosis and 0.61 +/- 0.001 for enteric yersiniosis. In the time course of pseudotuberculosis morbidity 2 periods were established. The first period (1974-1987) was characterized by the prevalence of epidemic outbreaks with a pronounced spring-summer rise in morbidity, mainly among children aged 3-6 years and 7-14 years in closed groups. The reasons of these epidemic outbreaks were established. The second period (1988-1994) was characterized by sporadic morbidity with seasonal winter-spring and summer-autumn rises involving children of all age groups both in closed groups and at home. The main trends in the system of epidemiological surveillance on Yersinia infections were determined, depending on the level and character of morbidity.